Heat exchangers



March 15, 1966 A. D. w. CORBET ET AL 3,240,266

HEAT EXCHANGERS Filed Feb. 13, 1963 3 Sheets-Sheet l 27 IT I March 1966 A. D. w. CORBET ET AL 3,240,265

HEAT EXGHANGERS Filed Feb. 13, 1963 3 Sheets-Sheet 2 March 1966 A. D. w. CORBET ETAL 3,240,265

HEAT EXGHANGERS 5 Sheets-Sheet 5 Filed Feb. 15, 1963 FIGS. I

6\ \\\T n /m/ United States Patent O 3,240,266 HEAT EXCHANGERS Alan Denys Wellington Corbet, Culchetlr, near Warrington, and Frederick Samuel Dickinson, Lowton, near Warrington, England, assignors to United Kingdom Atomic Energy Authority, London, England Filed Feb. 13, 1963, Ser. No. 258,277 Claims priority, application Great Britain, Mar. 13, 1962, 9,721/62 6 Claims. (Cl. 165158) This invention relates to heat exchangers and is primarily concerned with that kind of heat exchanger which employs a cluster of spaced parallel tubes end supported by tube plates and enclosed in a tubular shell, the assembly of tubes and tube plates hereinafter being termed a tube bundle.

In conventional heat exchangers of the hereinbefore specified kind it is usual to employ a tube bundle having relatively thick tube plates apertured to receive the ends of the tubes, the latter being swaged radially outwards to engage the walls of the apertures. Where it is required to ensure a fluid tight seal between the outer surface of the tubes and the walls of the apertures it is common practice to run sealing welds at the ends of the tubes round the joints between the tubes and the apertures. Heat exchangers having such tube bundles suffer certain disadvantages such as, for example, the difficulty they offer to the performance of satisfactory examination of the welds. Under certain conditions where the welds come into contact with corrosive fluids, undetected cavitational defects in the welds can secrete fiuid and subsequently develop major faults necessitating maintenance of the equipment which may not be practicable. Other disadvantages will later become apparent when the several advantages accruing to the present invention are described.

It is one object of the present invention to provide a heat exchanger of improved construction.

According to the present invention, a tube bundle for a heat exchanger comprising a cluster of spaced parallel tubes end supported by tube plates is characterized in that the tubes are secured to non-flanged ends of flanged ferrules, the ferrules being joined to the ends of the tubes and by their flanges to the tube plates.

Preferably the ferrules are forgings and the joints between the flangcs of the ferrules and the tube plates and between the ferrules and the ends of the tubes comprise butt welds.

According to another aspect of the invention a tube bundle for a heat exchanger is characterized in that the ends of the tubes are collectively adapted to engage a tube plate by rectilinearly flanged ferrules which are joined to the ends of the tubes and are joined together at the flanges to define a lattice-jointed structure, the lattice-jointed structure being joined to a tube plate.

The internal contours of the shell of a heat exchanger can be arranged to conform to the boundary defined by the lattice-jointed structure.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings wherein:

FIGURE 1 is a sectional view of one construction of heat exchanger,

FIGURE 2 is a plan view in section on line IIII of FIGURE 1,

FIGURE 3 is an enlarged fragmentary sectional view of a detail shown within the circle designated III of FIGURE 1, and

FIGURE 4 is a sectional plan view similar to FIGURE 2 and showing an alternative construction.

The heat exchanger shown vertically disposed in FIG- URE l is of composite construction and is fabricated from 3,240,256 Patented Mar. 15, 1966 stainless steel tube and plate. A tube bundle 1 comprises a cluster of spaced parallel tubes 2 end supported by tube plates 3. The ends of the tubes 2 are adapted to engage the tube plates 3 by means of forged flanged ferrules 4 which are butt welded at 5 to the tubes 2 and at their flanges 6 to the tube plates 3. I

In greater detail, the cluster of tubes 2 consists of one hundred and fifty tubes of 2" nominal bore having 3 /8" equilateral pitch spacing and the tube bundle 1 is joined to collars 7 of a fabricated shell 8 by butt welds 9 at the peripheries of the tube plates 3. A bellows 10 consisting of four convolutions 11 defines anexpansible section of the shell 8 to accommodate differential thermal expansion of the tube bundle 1 and the shell. The shell 8 extends beyond the tube plates 3 to define an upper chamber 12 and at the bottom a tube chamber 13 closed by a dished end 13:: having a downwardly extending branch pipe 14. A large branch pipe 15 on the shell 8 disposed intermediate the header plates 3 gives access to a shell chamber 16 bounded by the shell 8 and the tube plates, and two smaller branch pipes 17, 1% are located adjacent the lower tube plate 3. In the upper regions of the shell 8 adjacent the upper tube plate 3 there are branch pipes 19, 29, 21. Branch pipes 17, I3, 19, 20 communicate with the shell chamber 16 whilst the branch pipe 21 communicates with the regions of the shell immediately above the upper tube plate. The heat exchanger is adapted to be supported in the vertical position shown in FIGURE 1 by support brackets 2-2 attached to the shell.

Assembly of the heat exchanger is programmed so that all Welds can be radiographically examined as fabrication progresses, i.e. in the order: weld tube plates 3 to the collars 7, fabricate the shell over part of the length which extends between the collars 7, weld tube ends to ferrules 4, pass tubes with ferrules through tube plates and partially fabricated shell and the collars and the final shell tube plates 3 (commencing at the centre of the tube plates and thereafter progressing radially outwards) and finally, complete fabrication of the shell 8.

Access for radiographic examination of the welds in the tube plates is gained via openings left between the partially fabricated shell and the collars and the final shell welds are radiographed by inserting a rod anode in the outer tubes and placing a film on the outside of the shell.

In the construction shown in FIGURE 4, there is an array of square-flanged ferrules 27 for securing a cluster of tubes (not shown) to a tube plate 28. The ferrules are butt welded to the ends of the tubes as in the above first described embodiment and have square flanges 29 which are butt welded together to define a lattice-jointed structure thereby greatly facilitating welding and subsequent radiographic examination. The said structure is buttwelded to the tube plate 28 which is shaped to accommodate the said structure.

The first described construction of heat exchanger may be used as a second effect evaporator in apparatus for reducing the volume of, and recovering nitric acid from, radioactive efiiuent resulting from the processing of irradiated nuclear reactor fuel elements. Active liquor from a first effect evaporator is fed to the tube side of the second effect evaporator via the branch 14 and hot vapour from a first effect separator is fed to the shell chamber 16 via the branch 15. Vapour generated by heat exchange between the hot vapour in the shell chamber 16 and liquor in the tubes 2 passes via the upper chamber 12 to a second effect separator and liquor subsequently separated from the vapour in the second effect separator is returned to the second effect evaporator via the branch 14. The branch pipe 21 provides a drain (connected to branch pipe 14) for any liquor which becomes disentrained from the vapour passing to the second effect separator and unable to drain down the tubes 2 because of vapour velocity within them. Condensate from the shell chamber 16 is drained by Way of branch pipe 17. The branch pipe 19 is a vent from the shell chamber and branch pipes 18, 20 are outlets to vacuum pumps for removing non-condensible vapour.

In addition to facilitating satisfactory radiographic examination and other non-destructive tests of the welds of the described constructions of heat exchanger, further advantages accrue, namely: because each tube is rigidly attached to the tube plate at each end and thereby provides a stay capable of supporting the small areas of plate associated with it, a thinner tube plate can be used than is used in conventional heat exchangers and thereby effects an economy which is considerable in circumstances where the duties demand the use of expensive materials; improved flexibility resulting from the use of thin sheet material reduces internal stresses enabling materials which have a high resistance to corrosion (but are subject to cracking) to be used; by adapting the tubes to the tube plates by means of forged ferrules having grain flow parallel with that of the tubes and tube plates, laminations or inclusions at this connection are substantially eliminated as are crevices and pockets in the construction thereby minimising corrosion failure and subsequent maintenance; and, the higher heat transfer coeflicients available and greater heat transfer surfaces effect substantial savings in capital cost of the plant, compared with previous designs of fully radiographed heat exchangers employing jacket or coil heating.

We claim;

1. A heat exchanger comprising: a cluster of spaced parallel tubes, thin tube plates for end supporting said tubes, tubular elements securing each end of each of said tubes to each of said tube plates, said tubular elements each having a first end with a radially extending integral flange of thickness equal to the thickness of the tube plates and an unflanged second end secured to an end of one of said tubes by a butt weld, said integral flange extending substantially perpendicular to the longitudinal axis of said tubular element, said tube plates having apertures for receiving said flanges of said tubular elements, means defining continuous butt welds between peripheral edges of said flanges and the edges of said apertures whereby said tube plates are secured against longitudinal movement relative to said tubes, said means defining continuous welds extending over the thickness of the tube plates and flanges, said welds being adapted for radiovgraphic inspection by their disposition in outward displacement from said tubular elements, a tubular shell enclosing the assembly of tubes, tubular elements and tube plates and defining a chamber extending between the tube plates, closure members for said tubular shell defining a chamber bounded by one of said closure members and a tube plate at each end of the heat exchanger, and branch pipes attached to the shell and to at least one end closure member providing inlet and outlet ports to said chamber which extends between the tube plates and to the chamber bounded by the end closure members and tube plates.

- 2. A heat exchanger according to claim 1, wherein the tubular elements are forgings.

3. For a heat exchanger, a tube bundle comprising a cluster of spaced parallel tubes, thin tube plates for end supporting said tubes, tubular elements securing each end of each of said tubes to each of said tube plates, said tubular elements each having a first end with an integral radially extending flange of thickness equal to the thickness of the tube plates and an unflanged second end secured to an end of one of said tubes by a butt weld, said integral flange extending substantially perpendicular to the longitudinal axis of said tubular element, said tube plates having apertures for receiving said flanges of said tubular elements, means defining continuous butt welds between the peripheral edges of said flanges and the edges of said apertures whereby said tube plates are secured against longitudinal movement relative to said tubes by welds of a depth extending over the thickness of the tube plates and flanges and having symmetrical cross-section with longitudinal cross-sectional axes disposed parallel with the longitudinal axes of said tubular elements with said welds adapted for radiographic inspection by their disposition in outward displacement from said tubular elements.

4. A heat exchanger comprising a cluster of spaced parallel tubes, tubular elements each having a first end with a radially extending rectilinear flange and an unflanged second end, means defining a butt weld securing each of said tubular elements at its unflanged second end to each end of each tube, means defining butt welds for securing the peripheries of said rectilinear flanges of said tubular elements together to define a lattice jointed structure of rectilinear flanges at each end of the cluster of tubes, tube plates for end supporting said cluster of tubes, said tube plates having apertures for receiving said lattice jointed structures, means defining continuous butt welds between the peripheral edges of said lattice jointed structures and the edges of said apertures, a tubular shell enclosing the assembly of tubes, tubular elements and tube plates and defining a chamber extending between the tube plates, closure members for said tubular shell defining a chamber bounded by one of said end closures and a tube plate at each end of the heat exchanger, and branch pipes attached to the shell and at least one end closure providing inlet and outlet ports to said chamber which extends between the tube plates and to the chambers bounded by the end closures and tube plates.

5. A heat exchanger according to claim 4, wherein the tubular elements are forgings.

6. For heat exchanger, a tube bundle comprising a cluster of spaced parallel tubes, tubular elements each having a first end with a radially extending rectilinear flange and an unflanged second end, means defining a butt weld securing each one of said tubular elements at its unflanged second end to each end of tube, means defining butt welds for securing the peripheries of said rectilinear flanges of said tubular elements together to define a lattice jointed structure of rectilinear flanges at each end of the cluster of tubes, tube plates for end supporting said cluster of tubes, said tube plates having apertures for receiving said lattice jointed structures and means defining continuous butt welds between the peripheral edges of said lattice jointed structures and the edges of said apertures.

References Cited by the Examiner UNITED STATES PATENTS 2,000,653 5/1935 Wilkinson 82 2,203,357 6/1940 Kerr 122-365 2,368,391 1/1945 Young 165-134 X 2,549,093 4/1951 Huber 16581 X 2,763,923 9/1956 Webb 165-178 X 2,788,994 4/ 1957 Van De Wateren 285286 X 2,966,340 12/1960 Chapman 165180 X FOREIGN PATENTS 366,481 1/1932 Great Britain. 847,277 9/ 1960 Great Britain.

OTHER REFERENCES German printed application No. 1,105,894, printed May 4, 1961.

ROBERT A. OLEARY, Primary Examiner,

CHARLES SUK LO, xamine 

6. FOR HEAT EXCHANGE, A TUBE BUNDLE COMPRISING A CLUSTER OF SPACED PARALLEL TUBES, TUBULAR ELEMENTS EACH HAVING A FIRST END WITH A RADIALLY EXTENDING RECTILINEAR FLANGE AND AN UNFLANGED SECOND END, MEANS DEFINING A BUTT WELD SECURING EACH ONE OF SAID TUBULAR ELEMENT AT ITS UNFLANGED SECOND END TO EACH OF TUBE, MEANS DEFINING BUTT WELDS FOR SECURING THE PERIPHERIES OF SAID RECTILINEAR FLANGES OF SAID TUBULAR ELEMENTS TOGETHER TO DEFINE A LAT- 